In conventional compression-type refrigeration ariel/or air conditioning devices (including heat pumps) a refrigerant is compressed and circulated through the device while being subjected to alternating cycles of compression and expansion. In order to provide proper internal lubrication, particularly within the compressor, a lubricant is conventionally formulated with the refrigerant so that it can be circulated through the device along with the refrigerant.
A refrigerant which is frequently used, especially for automotive applications, is CFC-12, which is also known as R-12. The R-12 refrigerant is identified chemically as dichlorodifiuoromethane. The lubricants used with the R-12 refrigerant are conventional grade mineral oils which fall within the categories of paraffinic, naphthenic and alkyl benzene oils. These mineral oils are useful with the R-12 refrigerant because they have similar solubility characteristics so that they are miscible with the R-12 refrigerant. In order for such formulations to be effective, it is essential for the lubricant to be compatible with the refrigerant. The use of lubricants which are not compatible with the refrigerant results in unacceptable compressor life in compression-type refrigerators and air conditioners. This problem is particularly troublesome in automotive air conditioners because the compressors are often not separately lubricated and, consequently, a mixture of refrigerant and lubricant circulates through the entire system. It is well known that in order for a lubricant to be compatible with a refrigerant, the: lubricant must be miscible with the refrigerant.
Although the R-12 refrigerant has highly desirable physical properties which make it useful as a refrigerant, its present use is highly discouraged because of its role in the depletion of ozone in the upper atmosphere. The ozone depletion potential of R-12 and other CFC refrigerants has led to the imposition of many environmental regulations limiting the use of such refrigerants which are known to deplete the upper atmosphere of ozone. In 1987, the signatory nations to the Montreal Protocol agreed to freeze production and use of CFCs at 1986 levels and then to reduce the amounts to 50% over the ensuing ten years. In 1990, it was further agreed by the signatory nations to eventually end all use of CFCs. Consequently, research has led to the development of refrigerants to replace the CFCs, particularly CFC-12.
A suitable refrigerant for replacing R-12 or CFC-12 should have refrigeration characteristics which are comparable to the R-12 refrigerant and should have little or no deleterious effect on atmospheric ozone. One such refrigerant is known in the trade as HFC-134a or R-134a which is identified chemically as 1,1,1,2-tetrafluoroethane. One drawback in connection with the use of R-134a as a refrigerant in compression-type refrigerators and air conditioners is that the conventional mineral oil lubricants which are used with R-12 refrigerant are not miscible with the R-134a refrigerant. Thus, development of new technology to meet the Montreal Protocol and other regulations has also focussed on the development of lubricants which are miscible with the R-134a refrigerant.
The lubricants which have been developed for use with the R-134a refrigerant are synthetic lubricants which have been disclosed in the prior art. These synthetic lubricants, as well as the conventional additives for use therewith, are disclosed in the following patents, the specifications of which are incorporated herein by reference: U.S. Pat. Nos. 2,523,863 (Cook et al.); 2,807,155 (Williamitis); 4,248,726 (Uchinuma et al.); 4,267,064 (Sasaki et al.); 4,431,557 (Shimizu et al.); 4,755,316 (Magid et al.); 4,851,144 (McGraw et al.); 4,900,463 (Thomas et al.); 4,927,554 (Jolley et al.); 4,948,525 (Sasaki et al.); 4,959,169 (McGraw et al.); 4,963,282 (Jolley et al.); 4,971,712 (Gorski et al.); 4,975,212 (Thomas et al.); 5,008,028 (Jolley et al.); 5,017,300 (Raynolds); 5,021,179 (Zehler et al.); 5,021,180 (McGraw); 5,027,606 (Short); 5,032,305 (Kamakura et al.); 5,032,306 (Cripps); 5,037,570 (Gorski et al.); 5,053,155 (Mahler); and 5,137,650 (Kaneko).
The synthetic lubricants for use with R-134a refrigerant generally fall within the categories of polyalkylene glycols (PAG), polyol esters and polycarbonates. In particular, the lubricants listed below in Table 1, along with the generic chemical description and manufacturers are known for use with R-134a refrigerant.
TABLE I ______________________________________ AUTOMOTIVE AIR CONDITIONING LUBRICANTS: MINERAL OILS IDEMITSU DAPHNE Mineral oil from Apollo America; HERMETIC YN-9 Ford approved CFC-12 lubricant BVM-100N Mineral oil from BV Associates; General Motors approved CFC-12 lubricant SUNISO 5GS Naphthenic mineral oil from Witco AUTOMOTIVE AIR CONDITIONING LUBRICANTS: SYNTHETICS DF46XG PAG from Apollo America RO-W-6602 PAG from Union Carbide 2320F Polycarbonate from Mitsui RL-1681 Polyolester from Mobil ICEMATIC SW 100 Polyolester from Castrol OS96290 Polyolester from Lubrizol SONTEX SEZ-80 Polyolester from Pennzoil/DEA ANDEROL R-2845 Refrigeration lubricant from Huls America, Inc. EMKARATE RL-375 Polyolester from ICI 3202-20 Polyolester firom Henkel/Emery 70E-100-40 Polyolester from Unocal ______________________________________
The incompatibility between the aforementioned mineral oil lubricants also causes problems when introducing R-134a refrigerant/lubricant formulation into air conditioners or refrigerators, particularly automotive air conditioners, which already contain R-12 refrigerant/mineral oil formulations. This is because residual amounts of mineral oil and refrigerant typically remain in the system when changing an existing system from R-12 to R-134a. Thus, the incompatibility between the residual R-12 mineral oil formulation and the newly-introduced R-134 a/lubricant will be troublesome. Consequently, it would be highly desirable to be able to eliminate such incompatibility when retrofitting an existing R-12 system with R-134a. The synthetic lubricants which are used with R-134a refrigerant are significantly more expensive than the mineral oil used for the R-12. Thus, substituting R-134a for R-12 involves a considerable added expense due to the price differential between the synthetic lubricants and the mineral oil lubricants. Thus, it would be highly desirable if a lubricant could be formulated which is compatible with R-134a and which utilizes a significant amount of the cheaper mineral oil.